Magnetic storage drum



April 1962 A. H. BATTISON ETAL 3,028,584

MAGNETIC STORAGE DRUM Filed June 1, 1959 5 WM y ATTO/Q/VEVI States This invention comprises means in systems for magnetically storing data and information especially of the type employing a magnetic drum.

An important object of this invention is to provide a magnetic storage drum surface formation which increases the storage capacity of a drum of given size.

Another object of this invention is to provide a magnetic drum storage system including read-Write heads in which the drum is provided with a plurality of annular grooves displaced along its axial surface of a. form to minimize the effects of radial and axial run-out.

A still more specific object of the invention is to provide a magnetic storage drum with a plurality of annular grooves of V-shaped formation, cooperating with complementarily shaped recording heads for the purpose of minimizing the effects of axial and radial run-out.

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of examples, the principle of the invention and the best mode, which has been contemplated, of applying that principle.

In the drawings:

FEGURE 1 is a somewhat diagrammatic illustration in plan of a drum storage system in accordance with this invention with the center portion of the drum broken away to permit enlargement;

FIGURE 2 is a detailed view, partly in section and partly in elevation, showing the relationship of the recording head to the groove;

FIGURE 3 is a similar view from the edge of the structure of FIG. 2, looking endwise into a groove;

FIGURE 4 is a detail view, partly in section and partly in elevation with some parts broken away, of a modified system in accordance with this invention particularly adapted for use with drums having grooves which are small in cross-section;

FIGURE 5 is a diagrammatic view of the end of the recording head and a groove, illustrating some of the geometrical relationships involved in the assembly and the advantages gained therewith; and

FIGURE 6 is a structural geometrical illustration of the arrangement of FIG. 5 to facilitate describing the advantages of the conformations'used.

As will be readily apparent to those skilled in the art as this disclosure proceeds, the system includes a drum which is to be mounted in bearings for rotation on its longitudinal axis. As is Well understood from experience in this art, no matter how carefully the apparatus is constructed, there will be some axial and radial play or deviation in the position of the drum as it rotates with respect to the read-write heads which are fixed. These slight misalignments are referred to hereinafter as axial and radial run-out.

As will also appear hereinafter, the storage drum is of the type in which record tracks are in the form of annular grooves, so that the heads are fixed and one is provided for each groove.

As will also be apparent, the drum is normally made of magnetic material, but in some cases may be of nonmagnetic material and have magnetizable coatings on the faces of the grooves, as is well understood in this art.

The real substance of this invention will become more quickly exposed by starting this description with an exatent i we ' planation of what the drawings illustrate. As shown in FIG. 1, there is provided a magnetic drum 10, specifically a cylinder of magnetic material of suitable dimensions. Formed on the surface of this drum, in any suitable manner, are a plurality of annular grooves which in the case illustrated lie parallel to each other in planes at right angles to the axis of the drum. As shown, these grooves 12 are contiguous with no cylindrical spaces between them, forming a zig-zag surface in plan, as clearly illustrated. By this arrangement a maximum number of recording tracks are provided, but it will be appreciated that the invention is not limited to the contiguous spacing of the grooves.

There is also illustrated in FIG. 1, more or less diagrammatically, a series of read-write heads 14 which, as is well known in this art, constitute essentially soft iron magnetizable cores and magnetizing windings mounted thereon. As illustrated, because of the close spacing of the grooves, the recording heads 14 are circumferentially displaced, progressively in the case shown, so as to lie around the drum in a helical centerline. This arrangement is not essential to the advantages of this invention.

As illustrated in FIGS. 2 and 3, each recording head 10 consists of a U-shaped core 16, having a pair of symmetrically arranged legs 16 and 16 These legs are curved in elevation so as to be directed towards each other terminating, however, to form a magnetic air gap 17 within the associated groove 12. A coil 18 is mounted on the magnetic core at any suitable place for converting writing currents into data representing magnetic fields or any reading data bearing magnetic fields into corresponding electric currents, all as is well known in the art. As shown, the curved ends of the poles 16 and 16 of the core are complementarily shaped to form V-shaped heads 16' and i6", suitably dimensioned for the groove 12 associated therewith. As shown at R in FIGS. 2 and 3, the heads 15 and 16" can be grooved or undercut to shorten their faces which cooperate with the sides of the groove 12. As shown in FIG. 3, the root of the groove 12 at the point 13 is strain relieved by giving it a fillet formation.

The diagrammatic illustrations of FIGS. 5 and 6 are derived from this structure. As illustrated, a V-shaped 60 groove has been chosen by way of example. Similarly V the point or head end of each pole piece as illustrated in the case of the end 16", has its sides forming a 60 angle so that its faces are parallel to the sides of the groove 12. With this arrangement the read or write Signals occur on both faces of the head and groove.

Referring to FIG. 5, the faces of the groove are represented by the reference characters G and G and the faces of the head are respectively indicated at A and B. Thus With accurate centralization of the head in the groove the gaps between these face pairs are equal. Obviously, any play of the drum with respect to a head will vary these spacings increasing one and decreasing the other. However, within reasonable limits such as would be encountered with an apparatus of this type, these displacements will produce self balancing magnetic effects during either reading or writing. In other words, a greater gap on one side due to axial run-out will be balanced by a correspondingly similar gap on the other side of the head 16'.

With respect to radial run-out the variation in the gap disturbance at 13 or at the crest of the grooves will be minimized. The effects will vary as the cosine of the angle which for 60 equals 0.5, with the result that for example 0.002 radial run-out is eifectively only equal to 0.001.

With regard to storage capacity of the drum the following considerations apply. If we assume a drawing width of 0.050" for a cylindrical drum without grooves, the comparable 60 V track will require only one-half of the axial dimension of the track. This is well illustrated in FIG. 6, assuming that the sides A and B of the groove are each 0.025" in length. By simple geometric relations it is apparent that the distance C need only be 0.025. Thus with one-half the axial dimension required for a plain cylindrical drum it is possible to get recording lengths with the V groove equal to the 0.05" axial length required for a cylindrical drum. In a practical case the grooves would be cut to provide surface lengths G and G of 0.030" or thereabouts which will further minimize radial run-out effects using heads having the tips 16', 16 with side face dimensions of 0.025". With this arrangement a relatively large gap can be left at the V point 13, and at the crests of the grooves, as shown in FIG. 3, contributing a great deal to minimizing radial run-out effects at this point.

In summary, the advantages of this arrangement are:

(:1) Effective run-out will be decreased by a factor of 2, in the case of the example illustrated.

(b) Eifective recording area will be increased on the order of /3 for a given drum length (not the space left between tracks).

(c) Effective length reduction of the drum of 3/5 for the areas assigned to recording or reading (not spaces).

There is also a minor advantage in that only one strain or stress relief will be required with a V-shaped groove as previously suggested, as against two which are required with a single gap drum.

As a feature in miniaturization where very small grooves may be required, the construction of FIG. 4 is advantageous. With quite small grooves it becomes difiicult to build a satisfactory read-write head to coact with both sides of a single groove simultaneously. In that event the arrangement of FIG. 4 solves this problem by coacting with a single face of each of a pair of grooves. In the case of FIG. 4, the drum with its V-shaped grooves 12 is used as before. These grooves can be very small but have been enlarged to facilitate drafting. In this arrangement three heads 114, 120 and 122 are illustrated. Each head, like the head 114, having a magnetizable core 116 and the winding 118. Each pole of the core 116 will be forked, as illustrated in the case of the pole 116 In elevation the core 116 will have another pole corresponding to the pole 16 of FIG. 2, which will likewise be forked at the end. As illustrated, the pole 116 is provided with branches 116' and 116", which are dimensioned and shaped to cooperate one with the left face of one groove and the other with the right face of the adjacent groove. The corresponding forks of the head 120 will cooperate with the left face of the next groove to the left and with the other face of the groove with which the pole 116 cooperates. To complete the geometry of the situation, the left fork of the head 122 will cooperate with the other face of the groove with which the fork 116" cooperates. This is suflicient to illustrate how each head is constructed to cooperated respectively with one face of each of a pair of adjacent grooves. This arrangement makes it practicable to provide storage drums with very small V-shaped grooves having all of the advantages of this invention.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art, without departing from the spirit of the invention. It is the intention,t herefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. In an arrangement to minimize the effects of axial and radial run-out in a magnetic data storage system the combination comprising a drum rotatable on its axis, a groove formed in the surface of said drum defined by a pair of magnetizable surfaces and a read-write head having a pole piece projecting into said groove, said pole piece having its end of the same shape as that of the groove in cross-section to form an air gap at each of said groove surfaces so that both surfaces are used simultaneously to read in or read out information, said pole piece being spaced from said grooved surfaces at all points.

2. In the combination of claim 1, said groove being V-shaped in cross-section.

3. In the combination of claim 1, said groove and pole piece end being V-shaped in cross-section and the side faces of said pole piece end being shorter in a radial direction than the surfaces of the groove.

References tlited in the file of this patent UNITED STATES PATENTS 1,609,540 Goddard et a1. Dec. 7, 1926 2,361,753 Eilenberger Oct. 31, 1944 2,501,126 Howell Mar. 21, 1950 2,532,803 Faus Dec. 5, 1950 2,581,765 Mann et al. Ian. 8, 1952 2,844,665 Mann et a1. July 22, 1958 2,857,476 Kleiber Oct. 21, 1958 2,863,002 Brower Dec. 2, 1958 

